The present invention relates to rotors in synchronous machines. In particular, the invention relates to mounting rotor field winding and a field winding enclosure on a rotor.
Conventional generators have rotors with retaining rings to support field coil windings mounted on the rotor. Each rotor typically includes a cylindrical rotor core with axial slots to receive each coil turn of the field windings. During assembly, the winding is installed turn by turn into the slots of the rotor core. The field winding is typically assembled while it is being installed in the slots of the rotor core. The slots of the rotor receive the layers of the straight sections of the race-track shaped coil windings. The ends turns of the windings extend axially beyond both ends of the rotor core.
In conventional rotors, retaining rings are mounted over the end turns and on the rotor core. The retaining rings are short cylindrical structures that support the end turns with respect to the centrifugal forces that arise during rotor operation. The retaining rings are installed on the ends of the rotor core after the field windings are installed in the rotor slots. To reduce the circumference of the winding assemblies and rotor, a belt is wrapped around the winding assemblies to pull the winding coils together and eliminate clearances between the coil. During assembly, the metallic retaining rings are expanded by heat and then slid over the ends of the winding assemblies and rotor core. When the rings cool, they shrink to tightly fit on the rotor core. At normal operating temperatures, there is no clearance between the retaining rings and the end turns of the rotor windings.
A need has arisen for new techniques and enclosures for field windings on rotor cores. A cylindrical rotor enclosure has been developed that fits over the rotor and end-turns of the field windings. The enclosure supports the entirety of the windings against centrifugal forces. The enclosure may be, for example, a single cylindrical sheath or a plurality of rings that cover the windings and rotor.
In a first embodiment, the invention is a method for fitting a rotor enclosure over at least one assembly of field windings mounted on a rotor core, said method comprising the steps: applying a force to elastically reduce a circumference of the at least one assembly of field windings mounted on the rotor core, where the reduction in circumference is greater than a circumference reduction due to just eliminating clearances between adjacent end-turns of windings; generating a clearance between the field windings and the rotor enclosure due to the application of the force; axially sliding the rotor enclosure over the at least one assembly of field windings while the circumference is reduced, and releasing the force to allow the circumference of the at least one assembly of field windings to expand and cause the enclosure to tightly fit on the at least one assembly of field windings.
In another embodiment, the invention is a method of assembling a plurality of field windings and securing the windings on a rotor core comprising the steps of arranging a plurality of field windings in a winding assembly; mounting the winding assembly on the rotor core; deforming a cross-sectional shape of a cylindrical rotor enclosure or the end-turn of the winding to created a clearance between the enclosure and end-turn; sliding the deformed rotor enclosure over the mounted winding assembly, and releasing the deformation of the rotor enclosure after the enclosure is positioned over the winding assembly.